investigators accuse the men of killing a security guard earlier at the massachusetts institute of technology in cambridge. police say the pair car jacked a vehicle after that to make their escape. reuters reports they kept the driver hostage for about a half hour. officers caught up with them in nearby watertown. they engaged in a gunfight. residents heard shots and explosions. after police captured one of the suspects, they announced he had died. boston political identified the man on the run as the one in the white hat. they say he is 19 years old. the dead suspect was 26 years old. the brothers had been in the united states for several years. >> we believe this to be a terrorist. a man that's come here to kill people. we need to get him in custody. >> remain in your home, we're going through doing a serge, please stay in your homes, do not come out. >> authorities say people in watertown and surrounding communities should stay in doors until they get the all clear. authorities have also shut down public transportation in the area. mit, harvard, and boston university have canceled lectures